There are sensor system installations that require small sensor units because of restrictions in installation space or in order to enable the sensor units to be disguised. For example, in a monitoring or surveillance installation, it may be advantageous if the camera, microphone or any other required sensor such as a magnetic sensor, is small and thus can be disguised. One example of such installations is installations at ATMs (Automated Teller Machines), where at least one of the cameras generally is invisible or almost invisible.
Moreover, it may be advantageous to separate the sensor unit from the processing unit in a sensor system in order to facilitate exchangeability of the sensor unit without needing to replace the processing unit. For example the sensor unit may comprise limited logic capabilities and includes as little electronics as possible, and the processing unit may include the more power requiring electronics and the processing capability of the sensor system. The exchangeability may be advantageous for maintenance reasons or when the requirements of the sensor unit in the sensor system are changed.
When the processing unit is processing data from the sensor unit, calibration data defining specifics of the sensor unit is often required since each individual sensor unit may measure the sensed physical quantity differently compared to another sensor unit of the same sort.
A solution to this problem is described in U.S. Pat. No. 8,466,974B2 (O2Micro Inc.). In this document, an identification value of the sensor unit is stored along with the calibration data for the sensor unit, for example in a memory in the sensor unit. This identification value can then be used for identifying which sensor unit that is connected to the processing unit such that the processing unit knows which calibration data to use. A problem with this solution is that it must be ensured that the identification value is unique for each sensor unit, which may be difficult from a manufacturing point of view. Moreover, in the case the sensor unit is recalibrated, also the identification value needs to be updated and still be unique.